Ape, it's an imperfect world.
Can you prove they weren't pirates? Everything about them was suspicious enough for the RN to choose to investigate, and wow, they found weaponry consistent with what pirates have been using.
You're protestations, intentional or not, lead me to believe you are pro-pirate. What did they lose, really? They were detained, not held captive, not held for ransom. Their weapons were sent to the bottom of the gulf, big deal. Their masters will rearm them.
At worst, they got a soft paddling on the bottom like one gives a 2 year old, with a firm "No! Don't do that again!" and sent on their way.
Have you thought about the crewmen of the vessels hijacked already? Being held captive for no other reason than ransom money? All they were doing was their jobs. What about their families? Do you think about them, or are you so focused on the possibility that men whose behavior, location, and choice to arm themselves with weapons used for hijacking had their liberties "violated"?
Help me out here, I'm trying to see your side.